Electron gun memory



Jan. 2, 1968 c B. BRAHM 3,362,017

ELECTRON GUN MEMORY Filed Sept. 4, 1962 2 Sheets-Sheet l INVENTOR. CHARLES B. BRAHM BY gfl gm a 057M ATTOPNEYs Jan. 2, 1968 c B. BRAHM 3,362,017

ELECTRON GUN MEMORY Filed Sept. 1, 1962 2 Sheets-Sheet 2 INVENTOR. CHA RL E5 5. BQAHM ATTORNEYS United States Patent 3,362,017 ELECTRON GUN MEMORY Charles B. Brahm, Ellington, Conn, assignor to United Aircraft Corporation, East Hartford, Conn, a corporation of Delaware Filed Sept. 4, 1962, Ser. No. 221,247 12 Claims. (Cl. 340-173) My invention relates to an electron gun memory and more particularly to a storage device in which the information is both written and read by an electron beam tube.

In the prior art storage devices have included magnetic drums and tapes. Such storage devices have an extremely high capacity, but require appreciable readout time. For rapid read-out the prior art has turned to magnetic cores; but such devices have loW capacity. Storage devices employing magnetic drums, tapes and cores provide long term and permanent storage of information.

Cathode ray tubes have been employed in storage devices of the prior art. Information may be electrostatically stored on a dielectric mosaic. While electrostatic storage enables rapid access to the stored information the charges representing the information tend to leak off and become dissipated. Furthermore, the capacity of the electrostatic storage is limited.

Cathode ray tubes have further been employed in systems where the position of the beam is converted into a digital code and thus the device acts as an analogueto-digital converter. In one device of this type the beam impinges on a conventional phosphor screen to provide an illuminated spot. The light emanating from this spot is then focused by appropriate lens systems onto apertured plates embodying a convenient code; and photosensitive devices responsive to the light passing through the apertured plates provide a digital output. In another device of this type an apertured barrier plate embodying a convenient code is inserted within the tube itself. A plurality of collecting electrodes are placed behind the barrier plate remote from the electron gun. Since the electron beam can strike the collectors only Where the barrier is provided with apertures, the various currents collected by the electrodes provide a digital indication of the position of the beam.

One object of my invention is to provide an electron gun memory having rapid access.

Another object of my invention is to provide an electron gun memory having an extremely high capacity.

A further object of my invention is to provide an electron gun memory having permanent storage of information.

Other and further objects of my invention will appear from the following description.

In general, my invention contemplates the provision of an electron beam drilling tube having a beam of predetermined electron density profile. The information is stored by evaporting the material of a tape mounted within the tube so as to form apertures. The information is read by a beam of reduced energy which passes through the apertures to a metallic collector. Since beam deflection is used for both writing in and reading out of information, my system has a rapid access time. The capacity of my system is large since the tape may have appreciable length and may be moved to expose various portions to the electron beam. The storage is permanent since it depends upon the vaporization of material. The capacity of my system is further magnified by the feature that the size of the apertures can be varied by controlling the intensity of the writing beam. Thus, when reading by a beam of reduced intensity, the output current is a function of the size of the aperture and a third dimension Patented Jan. 2, 1968 is added. The information stored per unit of area may accordingly be increased by a factor of ten or even onehundred depending upon the stability and linearity of the reading and writing amplitude sensitive circuits.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are to be used in like parts of the various views.

FIGURE 1 is a schematic view of my electron gun memory system.

FIGURE 2 is a sectional view on an enlarged scale showing one form of recording tape.

FIGURE 3 is a sectional view on an enlarged scale showing another form of recording tape.

FIGURE 4 is an elevational view of a fragmentary portion of a recording tape in which information is digitally stored by discrete holes of various sizes.

FIGURE 5 is an elevational view of a fragmentary portion of a recording tape in which analogue information is stored on at least partially continuous tracks of varying width.

FIGURE 6 is a graph of the desired beam density profile for digital information stored by discrete holes of varying sizes as in FIGURE 4.

FIGURE 7 is a graph of the cross-axis beam density profile for continuous analog information stored by tracks of varying width as in FIGURE 5.

FIGURE 8 is a graph showing the relationship between the intensity of the writing beam and the output voltage produced by a reading beam of reduced intensity for beams having the respective density profiles of FIG- URES 6 and 7.

Referring now more particularly to FIGURE 1 of the drawings, I provide an electron beam drilling tube 10. Within tube 10 is mounted a tape 12 which passes over a conductive idler roller 16 and another idler roller 18 and thence to a tape drive mechanism 22. A collecting electrode 14 is placed behind tape 12 remote from the electron gun.

As will be shown in conjunction with FIGURES 2 and 3, at least that surface of tape 12 which is in contact with roller '16 is formed of a conductive material. Roller 16 is provided with aslip ring 16a which is engaged by a brush 17. Conveniently, roller 18 is formed of a nonconductive insulating material and the tape spools (not shown) of the tape drive mechanism 22 are electrically isolated so that brush 17 provides the only conductive connection to tape 12. Roller 18 drives an X transducer 19 which indicates the position of the tape. Preferably roller 18 is formed as a sprocket the teeth of which coact with chain-like slots or holes (not shown) spaced along one margin of the tape. This prevents slippage so that the output of X transducer 19 is accurate. An X position command 26 and the output of transducer 19 are differentially combined in a comparator circuit 28. The output of comparator 28 is coupled to the X deflection input of tube 10 and to the tape drive mechanism 22. The output of comparator 28 is further coupled to a hysteresis circuit 30 which provides an output only when the X deflection input of tube 10 exceeds predetermined limits defined by those positions of the beam approaching the boundaries of collector plate 14. The Y position command 24 is coupled to the Y deflection input of tube 10. I provide a source of variable potential 34 representing the information to be written or recorded, and a fixed source of reduced reading potential 36. I further provide a high voltage source 38 and a low voltage source 40. A single-pole, double-throw switch 42 is adapted to connect one of sources 34 and 36 to one input of an adding circuit 48. A single-pole, double-throw switch 43 is adapted to connect one of sources 38 and 40 to the accelerating anode of tube 10. Switches 42 and 43 are ganged together. In the writing position of the switches shown source 34 is coupled to adder 48 and the high voltage source 38 is coupled to the accelerating anode of tube 10. A fixed source 46 representing I is coupled to the other input of adder 48. The output of adder 48 is coupled through a gate 32 to the intensity input of tube 10. The output of hysteresis circuit 30 is coupled to inhibit gate 32. I provide a fixed source 50 representing E The signal on brush 17 and the output of source 50 are differentially combined in a subtraction circuit 54. The output of collector -14 and of source 50 are differentially combined in a subtraction circuit 52. Read-out voltages are obtained from either or both of subtracting circuits 52 and 54.

Referring now to FIGURE 2, in one form of my in vention the tape may comprise a thin sheet 12a of conductive material. The sheet 12a may have a thickness of the order of magnitude of one mil and may be formed of aluminum.

Referring now to FIGURE 3, in another form of my invention the tape may comprise a thin conductive sheet 121) which is coated with an insulating film 12c. Again, the conductive sheet 12b may have a thickness of the order of magnitude of one mil and may be formed of aluminum. The insulating film 120 may have a thickness of the order of magnitude of one-half mil. Conveniently, the insulating film 120 may be formed of a thermoplastic material. The recorded information may be erased by heating the tape so that the thermoplastic film 12c melts. When the film is heated to its melting point a smooth surface reforms. This permits the tape to be used several times.

If the tape is of the type shown in FIGURE 2 then an output may be obtained either from collector 14 or from brush -17. The output from collector 14 represents the electrons which pass through the tape apertures and impinge upon the collector. The output from brush 17 represents the electrons which fail to reach collector 14 and which instead impinge upon tape 12.

If the tape is of the type shown in FIGURE 3 then an output may be obtained only from brush 17 since no electrons penetrate the tape and arrive at collector 14.

Referring now to FIGURE 4, there is shown one embodiment of my invention in which information is digitally stored as discrete holes. Large amplitude signals from writing source 34 produce large holes 13a; whereas a small amplitude signal from writing source 34 produces a small hole 13b.

Referring now to FIGURE 5 there is shown another embodiment of my invention in which continuous analogue information is stored as slots or tracks 13c and 13d of varying width in accordance with the amplitude of the signal from the writing source 34. For this application, it is desirable that the tape speed be minimized. Accordingly, the tracks may be spaced along the X axis and may extend parallel to the Y axis.

Let us now determine the required beam density profile so that the output current collected when reading is proportional to the amplitude of the writing signal 34 where the information is stored digitally by discrete holes as in FIGURE 4. Let b be the normalized beam density for i=1 and let i be the intensity input. Let B be the resultant beam intensity. Thus:

Let C be the critical density of B which causes vaporization of the entire thickness of the conductive sheet 12a of FIGURE 2 or of the entire thickness of the insulating film 120 of FIGURE 3. Substituting C for B in Equation 1 and solving for i, we obtain It is desired that the output voltage e be proportional to the input intensity i and thus that The output voltage e will be proportional to the current which is collected either by plate 14 or brush 17 and thus (4) e:21rk frb(r) a'r where r is the radius of the hole as indicated by the dotted lines in FIGURES 2 and 3. Substituting Equations 2 and i k e 4 in Equation 3, we obtain (5) =21rk k frb(r)dr Solving this integral equation for b(r) we find il l i Substituting Equation 6 into Equation 4 and performing the integration we obtain From FIGURE 6 it will be seen that for the particular beam density profile b the output e and the radius r of the hole will be proportional to the input intensity i over the range from i:1 to i=2.

Let us now determine the required intensity profile so that the output current collected when reading is proportional to the amplitude of the writing signal 34 where the information is stored on a continuous analogue track as shown in FIGURE 5. It will be noted that x represents the cross-track axis and y represents an axis parallel to the track. Here we need only determine the intensity profile along the x or cross-track axis.

The output voltage e may be expressed as where x is the width of the track as indicated by the dotted lines in FIGURES 2 and 3.

Substituting Equations 2 and 9 in Equation 3 we obtain Solving this integral equation for b(x) we obtain Substituting Equation 11 into Equation 9 we find 12) /2Ck x 6 m From FIGURE 7 it will be seen that for the particular cross-travel intensity profile b the output e will be pro- 5 portional to the input intensity 1' over the range from i=1 to i: /2, since both e and i are proportional to the square-root of the cross-travel width x.

The intensity profile b of FIGURE 7 represents not the particular values of beam density but, instead, the values of the integral of beam density parallel to the y axis. The curve 8,; represents a beam density profile in the plane x=4; and the curve S represents a beam density profile in the plane x=8. It will be noted that S and S are similar, the y axis extent of 8.; being approximately /2 that of S and the peak amplitude of S at y= being approximately /2 that of S Accordingly if b(8)=fS dy=1.5, then [1(4): fS dy=3. There is no particular limitation on the beam density profiles of the various sections S(y). However, it is desirable that the various section profiles approach a rectangular or square-wave shape, having a small extent along the y axis, since this will enable more information to be presented per unit of length along a track. This means that for a given speed of scan along the y axis a higher frequency response may be obtained.

Referring now to FIGURE 8, there is shown a graph of e(i for FIGURES 4 and 6 and a graph of e(i for FIGURES 5 and 7. The broken curve represents the equation e(i)=i. It will be noted that e(i is coincident with e(i) from i=1, e=1, to i=2,'e=2 and that e(i is coincident With e(i) from i=1, e=1 to i= /2, e= /2. Accordingly, in FIGURE 1 circuit 46 should provide the value 1 :1 and circuit 50 should provide the value E =1 to transform the point i=1, e=l of FIGURE 8, which defines one boundary of the linear region, to the origin.

In FIGURES 2 and 3 it will be noted that I have shown the boundaries of the hole or track as having appreciable curvature corresponding generally to the beam density profile of FIGURE 6 and the intensity profile of FIG- URE 7. v

In operation of my electron gun memory in the Writing mode, switches 42 and 43 are in the position shown. Source 38 couples a high voltage to the accelerating anode of tube 10 and the source 34 of information to be recorded is coupled to adding circuit 48 Where it is combined with the offset voltage I The beam is deflected along the y axis by the Y position command 24. The X position command 26 is compared with the output of the X transducer 19 in circuit 28. The output of comparator 28 causes X deflection of the beam and also actuates the tape drive 22 which causes movement of the tape 12 until the output of comparator 28 is nulled and the beam is centrally positioned along the x axis. If the difference between the X position command 26 and the position of the tape 12 as represented by the output of the X transducer 19 is so great that the output of comparator 28 would cause positioning of the beam beyond the boundaries of collector 14 then hysteresis circuit 30 provides an output which inhibits gate 32. This prevents any signals from being coupled to the intensity input of tube 10. No reading or writing can occur until the tape drive mechanism 22 moves thedesired point of the tape within the field of View of the electron beam. When this occurs the output of comparator 28 will decrease sufliciently that hysteresis circuit 30 produces no output and gate 32 is rendered operative.

In the writing of discrete digital holes as in FIGURES 4 and 6 the information from source 34 may comprise either pulses of constant time duration but of variable amplitude or pulses of constant amplitude but of variable time duration. The intensity input i thus represents pulses of varying amplitude-time integral. In order to increase the speed of writing, the pulses provided by source 34 should be of short time duration. The minimtunhole diameter corresponding to r.=1 of FIGURE 6 may be .0004" and the maximum hole diameter corresponding to r=2 of FIGURE 6 will be .008". Thus I may provide 1,000 holes per linear inch, and 10 holes per square inch.

Since each hole may have between ten and one hundred discretely recognizable sizes depending upon the stability and linearity of the amplitude sensitive reading and writing circuits, the information density may be 10 binary bits per square inch. If the field of view of the electron beam (as defined by collector 14) is 5" x 5" representing 25 square inches, then the tape should have a y width of 5"; and 2.5 x10 binary bits of information are immediately available. It will be appreciated that the reading or writing of information on portions of the tape outside the field of view of the electron beam will not be instantaneous since some time is required for the tape drive mechanism 22 to position the tape.

In the writing of at least piece-wise continuous analogue tracks as in FIGURES 5 and 7 the amplitude-time integral of writing can be controlled either by varying the input from source 34 or by varying the scanning speed of the Y deflection input 24. A low rate of change in the output of circuit 24 provides a slow scanning speed and corresponds to a high intensity, while a rapid rate of change in the output of circuit 24 provides a high scanning speed and corresponds to a low intensity. Normally the rate of change of the output of circuit 24 is constant thus providing a constant scanning speed; and the intensity is controlled by the magnitude of the input from source 34. Thus I may record a conventional television signal providing 15,000 lines per second and having a frequency response extending to 4.5 megacycles which yields 300 bits of information per line. Tape 12 may again have a y width of 5". The minimum track width corresponding to x=2 of FIGURE 7 may be .0004" and the maximum track width corresponding to x=4 of FIGURE 7 will be .0008". Thus, I may provide 1,000 tracks per inch along the x axis. Since the analogue information is stored in continuous tracks rather than discrete holes, the density of information may exceed 2,000 bits per inch along the y axis. Thus, 10,000 bits may be stored on one track extending the full 5 width of the tape. This means that at least thirty lines of the television signal may be recorded on one track. It will be noted that the track will comprise thirty piece-wise continuous sections since no information will be recorded during line blanking. Where the tape is of the type shown in FIGURE 2, for reasons of mechanical rigidity, the tracks should not be continuous from one edge of the tape to the other. However, if the tape is of the type shown in FIGURE 3, then mechanical considerations pose no limitation; and continuous tracks may be cut from one edge of the tape to the other. In the recording of a television signal where line blanking is present and the tracks are only piece-wise continuous, then tape of the type shown in FIGURE 2 may be employed, since where line blanking occurs tape 12a will be left intact forming a bridge of metal which insures mechanical rigidity. Since thirty lines are provided per track, five hundred tracks must be written or read each second. Hence the speed of travel of the tape along the x axis must be 0.5" per second which represents 30 per minute.

In operation of my electron gun memory in the reading mode, switches 42 and 43 are moved to the right in FIG- URE 1. Source 40 couples a reduced voltage to the accelerating anode of tube 10; and source 36 couples a reduced voltage to adding circuit 48. If tube 10 employs magnetic focusing then a change in accelerating voltage applied to the anode will cause no defocusing of the beam when switch 43 is actuated. However, if tube 10 employs electrostatic focusing then an adverse defocusing effect may be prevented by coupling the signal at the armature of switch 43 not only to the accelerating anode of tube 10 but also tothe focusing anode as well. As will be appreciated by those skilled in the art, where a greatly re duced anode voltage is provided by source 40, then a normal beam current may be permitted to flow. However, if only high voltage source 38 supplies anode voltage and source 40 is eliminated, then the beam current must be greatly reduced. The heating effect or energy of the reading beam is proportional to the beam current and to the anode voltage. It is desired that for reading, the beam energy be greatly diminished so that no further evaporation of the material of the tape will occur. Source 50 causes the voltage E to be subtracted from the output obtained either at collector 14 or at brush 17 depending upon wheher the tape is of the type shown in FIGURE 2 or FIGURE 3. Thus the outputs from subtracting circuits 52 and 54 will be zero when reading information for which the voltage from the writing source 34 Was zero.

As previously indicated if the tape is of the type shown in FIGURE 2 then an output may also be obtained from brush 17 which represents those electrons which fail to reach collector 14 and instead impinge upon tape 12. Such output would, of course, have an inherent negative polarity. In order to transform this negative polarity output from brush 17 to the origin so that the output of subtraction circuit 54 is zero when reading information for which the voltage from writing source 34 was zero, it is necessary that the voltage of source 50 be greatly increased.

The chainlike holes along one margin of tape 12 which co-act with the teeth of sprocket 18 may be used for calibrating the position of the beam relative to the tape, and may further be used to calibrate the x axis deflection circuit. Similarly I may place holes along the other margin of the tape, so that the y axis deflection circuit may be calibrated. I may further provide various holes of different predetermined sizes to calibrate the amplitude sensitive circuits and more particularly to adjust the magnitudes of the voltages provided by sources 36, 46, and 50. Sources 34- and 38 must of course be calibrated or accurately regulated, since they determine the energy of the writing beam. However, accurate calibration or regulation of source 40 is not required, since it governs only the reduced energy of the reading beam and not its current density.

It will be seen that I have accomplished the objects of my invention. My electron gun memory has an extremely high capacity since the tape is very thin and a considerable length of tape may be stored in a small volume. For a tape having a five inch width, 5 X binary bits may be stored in each inch length of tape. My electron gun memory has an extremely rapid access time. For a tube having a field of view of 25 square inches, 2.5 X10 binary bits are immediately available with substantially no time delay. My electron gun memory provides permanent storage of information, since as long as the energy of the reading beam is held to low values, no further evaporation or degradation of stored information will occur due to reading; and the tape may be read as many times as desired.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details Within the scope of my claims without departing from the spirit of my invention. It is therefore to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention what I claim is:

1. An energy beam memory including in combination means for providing an energy beam, a thin body of material mounted in the path of the beam, means including the beam for forming apertures of various sizes in the body as a function of the amplitude of an input signal, and means responsive to passage of the beam through the apertures for determining the sizes thereof.

2. An energy beam memory including in combination means for providing an energy beam, a body of material mounted in the path of the beam, means including the beam for evaporating various differing quantities of material from the body as a function of the amplitude of an input'signal, and means responsive to the beam for determining the quantities of material evaporated.

3. An electron gun memory including in combination an electron gun providing a beam and having a deflection input, a recording medium mounted in the path of the beam, means for positioning the recording medium, means for indicating the position of the recording medium, means providing a positional command, means for comparing the positional command with the indicated position of the recording medium to provide a difierence signal, and means responsive to the difference signal for controlling the positioning means and the deflection input.

4. An electron gun memory as in claim 3 which further includes means responsive to a diiference signal exceeding predetermined limits for providing an inhibiting signal.

5. An electron gun memory for reading and writing information including in combination an electron gun providing an electron beam, a thin body of material mounted in the path of the beam, means for forming apertures of varying sizes in the body to record informa tion, the recording means comprising means for varying the intensity of the beam, means for reading the recorded information, the reading means comprising means for maintaining the intensity of the beam constant and means for collecting a variable portion of the beam current as a function of the size of an aperture, and the beam having such electron density profile that the reading beam current collected varies as a linear function of the intensity of the recording beam over an appreciable range of intensities thereof.

6. An electron gun memory including in combination an electron gun providing an electron beam, a body of conductive material mounted in the path of the beam, means including the beam for evaporating various difiering quantities of material from the body to record information, and means responsive to beam current for reading the recorded information, the reading means including means making a conductive connection with the body.

7. An electron gun memory including in combination an electron gun providing a beam, a thin tape mounted in the path of the beam and having equally spaced holes along its length, a rotatable idler sprocket having teeth which co-act with said holes, transducing means responsive to rotation of the sprocket for indicating the position of the tape, and means independent of the idler sprocket for driving the tape.

8. An electron gun memory system including in combination an electron gun providing a beam, a thin tape formed of a conductive material which is coated with an insulating film, the tape being provided with equally spaced holes along its length, means including a rotatable sprocket having teeth which co-act with said holes for positioning the tape in the path of the beam with the film adjacent the gun, means responsive to rotation of the sprocket for indicating the position of the tape, means including the beam for evaporating apertures in the film to record information, and means responsive to the beam and including means making a conductive connection with the conductive material of the tape for reading the recorded information.

9. In an electron gun memory for reading and writing information in the form of discrete circular apertures, an electron gun providing an electron beam of circular cross-section which satisfies the equations and said apertures having various diameters a such that 2N d 2M, where b is the electron density and r is the distance from the center of the beam, where K is a constant, and where M and N are respective maximum and minimum limits.

10. In an electron gun memory for reading and writing information in the form of an elongated aperture having a longitudinally extending center line, a electron gun providing an electron beam which satsfies the equations and said aperture having a variable width w such that 2N w 2M, where b is the electron density integral along a parallel to the center line and x is the distance from the center line to such parallel, where K is a constant, and where M and N are respective maximum and minimum limits.

11. A method of writing and erasing information in a coating comprising a thermoplastic film of a certain uniform thickness including the steps of evaporating apertures in the film to record information and heating the apertured film to a temperature sufiicient to produce a reduced uniform thickness to case said information.

12. A method of Writing and erasing information in a thermoplastic film including the steps of evaporating apertures in the film to record information and heating 10 the apertured film to its melting temperature to case said information.

References Cited UNITED STATES PATENTS 2,843,799 7/1958 Hook 31512 2,919,377 12/1959 Hanlet 31512 2,294,149 8/ 1942 Kline 1785 2,935,369 5/1960 Megnone 346-135 2,819,380 1/1958 Eaton.

3,151,231 9/1964 Steigerwald 219121 2,425,003 8/1947 Potter 346-74 3,072,889 8/1947 Willcox 340173 2,985,866 5/1961 Norton 347--173 3,226,696 12/1965 Dove 340-173 TERRELL W. FEARS, Primary Examiner.

S. SRAGOW, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,362,017 January 2, 1968 Charles B. Brahm It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 9, line 15, and column 10, line 1, for "ease", each occurrence, read erase column 9, line 17, before "thermoplastic" insert coating comprising a Signed and sealed this 11th day of February 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

9. IN AN ELECTRON GUN MEMORY FOR READING AND WRITING INFORMATION IN THE FORM OF DISCRETE CIRCULAR APERTURES, AN ELECTRON GUN PROVIDING AN ELECTRON BEAM OF CIRCULAR CROSS-SECTION WHICH SATISFIES THE EQUATIONS 